This result is an extension of Proposition 1 in [1]}
in which the case \(r_0=\rho _0\)  and \(\Omega =0\)  is addressed (whose proof follows the same lines as the one
of Proposition REF ).
It shows that, if we deal with an integral of \(\widetilde{M}^{\varepsilon }_2\)  against a bounded function,
then we can replace \(\widetilde{M}^{\varepsilon }_2\)  by the right-hand side of (REF ) without the \(R^{\varepsilon }_2\)  term
up to a negligible error when \({\varepsilon }\)  is small. Note also that the result shows that the fourth-order moment
\(M_2\)  can be expressed in terms of second-order moment \(A\)  in (REF ) and in terms of the source field,
which can be seen as a `quasi-Gaussian property' [1]}.
